I had some little PC boards made for a new
set of Joule Thiefs to add to my collection. Above the right eye is a
temperature sensitve thermistor. As the temperature rises, the
resistance gets less. The blink rate will increase . In the
freezer, the blink rate is once every 10 seconds. At normal room
temperature the blink is about once per second and in the sun, the leds
stay on.